I poked around on radioshack.com but couldn't find a link to the battery packs. But you cut off the PC power supply connectors and replace them with those connectors for 9V batteries, which fit on the 12V battery packs of AA batteries. I'll try to come up with the link so you can see what I'm talking about. Or you could ust go to Radio Shack and poke around in the bins in the back, gotta love that you can still do that.

I won't promise that the UV Lazer LEDs will light up what you want properly. I tried one a couple years ago out of curiosity and it looked OK, but I'll be interested to hear what anyone does with them.

Not sure the UV ones will really light up a lot, but they're worth checking out. I especially like that these are flat so you can hide them under whatever you're wearing.

What kind of adapter would you have to use to make them wearable? They're designed to hook into PC/car/boat power sources.

The UV ones are for blacklight- they'd work great with fluorescent paints.

Radio Shack has battery holder that hold 8 AA's. They have a 9volt style connector on the pack's top so you can easily disconnect your creation from the pack. You could use it in place of a switch even by just snapping it on when needed. They have the 9volt connectors in 2 packs as well. If using rechargeable batteries you'll get a nominal 10.8 volts (closer to 11v in actuality). That should be enough to run most 12volt items at almost full strength. Some items may be picky but not many. Just running lights or LED's? Shouldn't be a problem. Small 1 to 2 amp-hour gel cell batteries are fantastic! They'll easily recharge with small solar panels during the day. Find em online at battery retailers. Beiter Battery has good prices as does batteries plus.

He's a mystery wrapped in a riddle, inside an enigma, painted in hot pants. - SavannahPropane ToysHow to do it wrong:

Eric wrote:Radio Shack has battery holder that hold 8 AA's. They have a 9volt style connector on the pack's top so you can easily disconnect your creation from the pack. You could use it in place of a switch even by just snapping it on when needed.

Yes, I do that, but you have to be careful to connect them correctly. The LEDs would burn out if you tried to connect the batteries backwards.

Tell more about gel cells. How small do they get? I'm finding a lot of big, heavy ones but not something you could put in your pocket.

Eric wrote:Yes, I do that, but you have to be careful to connect them correctly. The LEDs would burn out if you tried to connect the batteries backwards.

They shouldn't. LEDs are Diodes (the D in LED). Diodes conduct current one way, but block it the other way. So if you connect an LED the wrong way around, it will block and no current will flow. It will not get damaged. (Unless the voltage was very high, but then you'd probably fry the the right way around too).

Now, if you buy some assembly with several LEDs that has any electronics in there, you could fry those if you connect it with the wrong polarity. But LEDs will handle wrong polarity without damage.

Last edited by SnowBlind on Fri Jul 15, 2011 5:25 pm, edited 1 time in total.

ricochet wrote:I poked around on radioshack.com but couldn't find a link to the battery packs. But you cut off the PC power supply connectors and replace them with those connectors for 9V batteries, which fit on the 12V battery packs of AA batteries. I'll try to come up with the link so you can see what I'm talking about. Or you could ust go to Radio Shack and poke around in the bins in the back, gotta love that you can still do that.

I won't promise that the UV Lazer LEDs will light up what you want properly. I tried one a couple years ago out of curiosity and it looked OK, but I'll be interested to hear what anyone does with them.

Check out the link that I posted above to All Electronics. They sell all kinds of battery packs, and some with 9v snap type connectors, plus the snap connectors themselves.

Check out the 4-AA pack that's wired for 3v. Since pretty much all LEDs like 3v, you could wire them all in parallel and not have to use a resistor. Super quick wiring. I've also had great luck with this LED supplier on Ebay. Dirt cheap, and they are to my door in like 10 days from China. I've wired up exactly 1360 of these now.. Check his other auctions for any other colors.

OK, so I don't know a whole lot about LED's. Hopefully you can help me figure some stuff out.

From the previous post, you said most LED's like 3v, DC? yes?The UV LEDs on the Ebay link has that little chart for voltage, it says the UV like 3-3.4v. So, if I use 4 AA batteries in 2 pairs. 2 AA in each pair in series, to get 3v. Then each pair in Parallel, to stay at 3v but longer life. I should be able to just run leads to each LED right? Will I need to run the leads from each LED back to the batteries, or will I be able to run the LED's in series (daisy chain)?

Why don't ya stick your head in that hole and find out? ~pieholePlan for the worst, expect the best. Make the most out of it under any conditions. If you cannot do that you will never enjoy yourself. ~CrispyDave

illy dilly wrote:OK, so I don't know a whole lot about LED's. Hopefully you can help me figure some stuff out.

From the previous post, you said most LED's like 3v, DC? yes?The UV LEDs on the Ebay link has that little chart for voltage, it says the UV like 3-3.4v. So, if I use 4 AA batteries in 2 pairs. 2 AA in each pair in series, to get 3v. Then each pair in Parallel, to stay at 3v but longer life. I should be able to just run leads to each LED right? Will I need to run the leads from each LED back to the batteries, or will I be able to run the LED's in series (daisy chain)?

That is the minimum voltage. There is likely a maximum voltage too... you also need to pay attention to the current rating. You should buy a resistor to put in line with the LED to limit the current so that you don't burn the LED out. Here is a calculator you can use http://www.sengpielaudio.com/calculator-ohmslaw.htm or if you are old fashioned Voltage = Current * Resistance However, I think that if you use the exact voltage you might not need a resistor? Not too sure... resistors are cheap, just go with a resistor.

I am pretty sure you will need to run the LEDs in parallel. Each LED will cause a voltage drop and thus any LED after that one in series will get a lower voltage and thus be dimmer.

Typical drive current is 20mA You can drive them higher for increased voltage but life will suffer at a non-linear rate the higher you go. Plug these numbers into this calculator: http://ledcalculator.net/It will show you either a wiring diagram or schematic, your choice. There are many calcs online. Electronic creations are much easier than you'd believe. It's just like any artform. Start off painting by numbers and eventually you can start from a blank canvas. There are plenty of soldering FAQ's and instructions online. MAKE magazine is a great source of ideas and instruction. Find out if there are "hackspaces" / "hackerspaces" in your city. People of all skills and skill levels get together and collaborate or build individually and they are glad to help you become addicted.

Instructables is a terrific resource for not only electronics but everything else as well.[url]http;//www.instructables.com[/url]

A handy thing to do that is fun too is to deliberately wreck a few or a few dozen LED's. Drive them at increasingly higher current by reducing the value of the current limiting resistor or using a potentiometer. You'd be amazed how bright they'll get!

He's a mystery wrapped in a riddle, inside an enigma, painted in hot pants. - SavannahPropane ToysHow to do it wrong:

illy dilly wrote:OK, so I don't know a whole lot about LED's. Hopefully you can help me figure some stuff out.

From the previous post, you said most LED's like 3v, DC? yes?The UV LEDs on the Ebay link has that little chart for voltage, it says the UV like 3-3.4v. So, if I use 4 AA batteries in 2 pairs. 2 AA in each pair in series, to get 3v. Then each pair in Parallel, to stay at 3v but longer life. I should be able to just run leads to each LED right? Will I need to run the leads from each LED back to the batteries, or will I be able to run the LED's in series (daisy chain)?

That is the minimum voltage. There is likely a maximum voltage too... you also need to pay attention to the current rating. You should buy a resistor to put in line with the LED to limit the current so that you don't burn the LED out. Here is a calculator you can use http://www.sengpielaudio.com/calculator-ohmslaw.htm or if you are old fashioned Voltage = Current * Resistance However, I think that if you use the exact voltage you might not need a resistor? Not too sure... resistors are cheap, just go with a resistor.

I am pretty sure you will need to run the LEDs in parallel. Each LED will cause a voltage drop and thus any LED after that one in series will get a lower voltage and thus be dimmer.

As always...Workinonit

Yeah looking at the ebay page, it says 3v min-3.2v max. It doesn't say what the voltage drop is. But screw it. For 5 bucks and free shipping, I'll hook em up to some AA batteries. Throw the multi-meter on them and see what happens. LOL.

Yeah I always remember it "Power Is Valuable" and "Value Is Resistance" so P=I x V and V=I x R where P is Power, I is current, V is volts. And in the sister equation R is Resistance or Ohms. And then from those two equations you can do all sorts of algebra to figure out other stuff. And that is pretty much the extent of my electrical engineering daily routine.

Why don't ya stick your head in that hole and find out? ~pieholePlan for the worst, expect the best. Make the most out of it under any conditions. If you cannot do that you will never enjoy yourself. ~CrispyDave

When you're hooking up a bunch of + sources to the same daisy chain, there is no voltage drop as you go. Every + contact is seeing the same amount of voltage as the previous one. Think about it. Wire goes to the + and wire leaves the + to the next +.. so on and so forth.

1 AA or AAA battery is 1.5 volts, so 2 would be 3 volts.. or you can get one of those 4 AA holders that are wired to give 3v.. just they would last longer using 4 AAs instead of 2. You can run LEDs that require 3.2-3v off of less.. they will just get dimmer as the night goes on.

They really are so very easy to work with. Check out my thread about the pants that I'm building. Once you play with them for a few minutes its like.. dude.. I'm sticking these things everywhere. They're so easy. I'm making my girl a skirt with like 30 purple LEDs embedded using one of the 4 AA/3v holders, and just daisy chaining them together. Push the LED through the fabric, and bend the contacts outwards and they stay in perfect. So.. easy. Sew in a little pouch in the back to hold the battery pack and wire it all together with some 22 gauge stranded hookup wire from Radio Shack or wherever. Solder the joints for best durability.

Eric wrote:Yes, I do that, but you have to be careful to connect them correctly. The LEDs would burn out if you tried to connect the batteries backwards.

They shouldn't. LEDs are Diodes (the D in LED). Diodes conduct current one way, but block it the other way. So if you connect an LED the wrong way around, it will block and no current will flow. It will not get damaged. (Unless the voltage was very high, but then you'd probably fry the the right way around too).

OK, I did hesitate when I was writing that. I have burned some out but not for a long time, maybe I had done something else. So maybe now I'm just superstitious about it. Hmm, I should try that again.

illy dilly wrote:OK, so I don't know a whole lot about LED's. Hopefully you can help me figure some stuff out.

From the previous post, you said most LED's like 3v, DC? yes?The UV LEDs on the Ebay link has that little chart for voltage, it says the UV like 3-3.4v. So, if I use 4 AA batteries in 2 pairs. 2 AA in each pair in series, to get 3v. Then each pair in Parallel, to stay at 3v but longer life. I should be able to just run leads to each LED right? Will I need to run the leads from each LED back to the batteries, or will I be able to run the LED's in series (daisy chain)?

LEDs are highly non-linear, that means you can't just do the usual V = IR to figure things out. You could in theory run them without a resistor, but that would only work if you have the exact right voltage. Small changes in voltage can result in big changes in current, and damage them. So unless you are using a special driver, which keeps the current constant, you should add resistor to limit the current.

Other than adding the resistor, you can do the battery setup you describe. If you run two LEDs in parallel, each should get their own resistor. If you run them in series (I assume that's what you mean by daisy chaining), you can run them with a single resistor. However, then you need to double the voltage, since each LED will drop 3 volts (or whatever their forward voltage is). You should also have some headroom, since the resistor will eat some of your voltage. (So if the forward voltage is between 3 and 3.4, you might not be able to run them of 2 AAs. You'd then have to use 3 AAs and drop the difference over the resistor.)

Play with the numbers. Once you see it with your own eyes, it's much easier.

Also.. LEDs are not as fragile as you are making them out to be. They will only get dimmer as the voltage drops out.. not spontaneously combust. Running multiple LEDs off of 2 AA batteries is not going to harm anything..

By "daisy chaining", I mean having multiple LEDs.. right? A wire comes from the positive source of the battery and goes to the first positive lead on the LED. A wire then connect to the first positive pin, and then goes to the second LED positive pin.. so on and so forth. A parallel circuit.. just linking them all up by common positive and negative wires from one to the next like a big chain.

See, and to me, Daisy Chain means run in series. Funny how not specific terms can be flip flopped to mean two different but similar things.

Why don't ya stick your head in that hole and find out? ~pieholePlan for the worst, expect the best. Make the most out of it under any conditions. If you cannot do that you will never enjoy yourself. ~CrispyDave

How to properly rig up your LEDs so you don't burn them out and so you can power up multiple LEDs at your desired brightness:

Assume your battery has voltage V+

Assume your LED has a "forward voltage" V_f and that V+ is greater than V_f

Assume that your LED has a "maximum continuous current" of I_c

Your goal: find a proper resistor with value R that will give you [i]I_c so that you have the brightest LED for your battery (without burning the LED out).[/i]

The resistor limits how much current the LED receives. With too much current the LED can burn out. The LED is connected in series (end to end) with the resistor so that the resistor limits the current passing through both.

Compute how much voltage you will have across your resistor. This is your battery's voltage (V+) minus the forward voltage of your LED (V_f):

V_r = V+ - V_f

Determine the value of the resistor R, using Ohm's law. This involves your max current (I_c) and the resistor voltage (V_r):

(please note that you should probably buy your LEDs from eBay, as $0.95 from Sparkfun is a very expensive LED.)

Battery pack: 4xAA batteries

V+ = 4 x 1.5V = 6V

Compute V_r:

V_r = 6V - 3.4V = 2.6V

Compute the necessary resistance R:

R = 2.6V / 0.02A = 130 ohm

Great, now choose a resistor that is close to that value. We're in luck, because 130ohm is a pretty standard value at parts shops like Mouser.com. I would buy 100 at a time, since it's only $1.80 for 100 compared to $0.10 in singles.

A word on resistor wattage:

If you're powering high powered LEDs, you might need to have resistors that can handle that much power. Resistors have power ratings (in watts), usually 1/8W, 1/4W, 1/2W, 1W, etc.

You can compute the wattage as follows:Power(Watts) = I_c * I_c * R

Example using the above:0.02A * 0.02A * 130ohm = 0.052W

So a 1/4 W or 1/8 W resistor will do.

Paralleling your resistors:

Simply attach the LED + resistor series-pairs as described above to the same battery voltage. E.g.

OK so then from what you're saying, if I'm using 4 AA batteries, and these UV LEDs http://cgi.ebay.com/50-pcs-5mm-Round-UV-purple-Superbright-LED-Light-/110619752690?pt=LH_DefaultDomain_0&hash=item19c17378f2 (from a previous post)In the chart on the page it shows they have a forward voltage of 3.2 and everything else is rated at 20mA. So if:6-3.2= 2.8 then 2.8/.02= 140ohm. I'm with ya up to there. But when I plug the same info into the LED Wizard previously mentioned with lets say 10 LEDs, it tells me I need a 150ohm resistor.Help me out here. Both 140 and 150 ohm resistors seem to be pretty easy to find, but which would be better?

Why don't ya stick your head in that hole and find out? ~pieholePlan for the worst, expect the best. Make the most out of it under any conditions. If you cannot do that you will never enjoy yourself. ~CrispyDave

10 ohms isn't going to make a visual difference, and your voltage will drop on you as you use them.. so go 140ohm. The wizard must just be doing some rounding.

Purple LEDs are also very dim, FYI. I've got a bag of 1000 here that I was going to use until I saw how dim they were. Now they are going on the girls outfit embedded in the long white shag fur for a cool purple glow..

Also, that seller is great FWIW. I've order 5 different orders through him, and they are always at my door within like 10 days.